Behind the scenes

Knotgrass may refer to several species of the Polygonum genus found in England and Europe. It is most likely Polygonum aviculare, which was believed to halt the growth of animals and was mentioned as such in the works of Shakespeare.[1]

The use of knotgrass in the Polyjuice Potion was chosen by J. K. Rowling to represent "being tied to another person".[2]